Measurement of sperm motility (fraction of motile cells) is of considerable importance in the animal breeding market. The reason is that motility is a measure of the animals breeding effectiveness, since only motile sperm can fertilize the ovum. For a given number of sperm required per insemination dose, a higher motility means that the sample can be diluted more and therefore spread around to more females for breeding. This reduces the breeding cost and increases breeding efficiency. Therefore accurate determination of sperm motility is economically important.
Capillary-loaded chambers are frequently used for sperm sample examination. A chamber is created by placing a coverslip onto a microscope slide. The area between the slide and the coverslip is the chamber. Typically (e.g. in the Leja-4 chamber), a glass coverslip is fixed in position by ink strips, at a separation of 20 μm above a glass microscope slide. The 20-μm space thus formed between the two sheets of glass is divided into chambers (usually 2 or 4), each of which may be independently used for sperm sample analysis. The sperm sample is introduced at the entrance, and capillary action in the 20 μm gap sucks the sample into the chamber. It is then examined by microscope, and may be used for computer-assisted sperm analysis (CASA), for example with the IVOS analyzer. The IVOS measures the position of each sperm in a field of view. It then repeats the measurement at intervals of 1/60 seconds, thus determining static and motile sperm count and velocity. The advantage of the capillary-load chamber is that it measures concentration of motile sperm cells accurately, allows rapid loading and analysis and is disposable.
A radially-loaded chamber (e.g., the Makler chamber) uses four posts to maintain a coverslip 10 μm above the slide surface, and is loaded by placing a drop on the sample platform. The cover is then placed on top of the platform. In contrast to the capillary-loaded chamber, the sample then spreads radially and is not loaded by capillary action. The sample is then examined visually or by CASA. A defect of the radially-loaded chamber is that the coverslip is not constrained and can therefore rise up, increasing the chamber depth. A particle only one micron in diameter on the posts will cause an error of 10% in the concentration calculation from the radially-loaded chamber. Moreover, after use, the chamber has to be cleaned, and its operation is consequently slower and the resulting concentration calculation is less accurate than the disposable capillary-loaded chambers.
Recently it has been found that sperm samples loaded into a radially-loaded chamber show higher motility than in the capillary-loaded chamber. The sperm sample consistently shows approximately 15% higher initial motile fraction in the radially-loaded than in the capillary-loaded chamber. Sperm velocity and other sperm motion parameters are not significantly altered. Since successful animal breeding depends on accurate motility measurement, it is important to determine if the decrease in motility in the capillary-loaded chamber is an artifact, and, if so, whether it can be eliminated. Possible causes include the greater chamber depth, potential toxic effects in the fixed-coverslip chambers, and possible damage to sperm during the capillary inflow loading phase.
Accordingly, it is desirable to provide an improved disposable capillary-loaded chamber design which provides an accurate and reliable sperm motility count and allows for rapid loading and analysis. The embodiments of the present invention represent an improvement to the capillary-loaded chamber design which prevents the reduction in motility observed in comparison to the radially-loaded chamber. It therefore increases the accuracy of sperm analysis using capillary-loaded chambers and allows more accurate and efficient animal breeding to be practiced.